[patch] libstdc++/61947 fix constructor ambiguity in std::tuple

[Jonathan Wakely <jwakely at redhat dot com>]

This adds a tag parameter to the tuple base class constructors that
are used to implement uses-allocator construction but currently only
have a single parameter, ensuring they are not viable candidates when
calling a single-argument constructor.

Tested x86_64-linux, committed to trunk. I plan to fix this on the
release branches too at some point.

commit 007f346ea8b17e323fedba0c425f80ee3f8fddee
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Jul 29 16:35:10 2014 +0100

    	PR libstdc++/61947
    	* include/std/tuple (_Head_base): Use allocator_arg_t parameters to
    	disambiguate unary constructors.
    	(_Tuple_impl): Pass allocator_arg_t arguments.
    	* testsuite/20_util/tuple/61947.cc: New.
    	* testsuite/20_util/uses_allocator/cons_neg.cc: Adjust dg-error line.

diff --git a/libstdc++-v3/include/std/tuple b/libstdc++-v3/include/std/tuple
index ef8aa5a..6c1032f 100644
--- a/libstdc++-v3/include/std/tuple
+++ b/libstdc++-v3/include/std/tuple
@@ -61,21 +61,22 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       constexpr _Head_base(const _Head& __h)
       : _Head(__h) { }
 
-      template<typename _UHead, typename = typename
-	       enable_if<!is_convertible<_UHead,
-	                                 __uses_alloc_base>::value>::type>
+      constexpr _Head_base(const _Head_base&) = default;
+      constexpr _Head_base(_Head_base&&) = default;
+
+      template<typename _UHead>
         constexpr _Head_base(_UHead&& __h)
 	: _Head(std::forward<_UHead>(__h)) { }
 
-      _Head_base(__uses_alloc0)
+      _Head_base(allocator_arg_t, __uses_alloc0)
       : _Head() { }
 
       template<typename _Alloc>
-	_Head_base(__uses_alloc1<_Alloc> __a)
+	_Head_base(allocator_arg_t, __uses_alloc1<_Alloc> __a)
 	: _Head(allocator_arg, *__a._M_a) { }
 
       template<typename _Alloc>
-	_Head_base(__uses_alloc2<_Alloc> __a)
+	_Head_base(allocator_arg_t, __uses_alloc2<_Alloc> __a)
 	: _Head(*__a._M_a) { }
 
       template<typename _UHead>
@@ -106,21 +107,22 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       constexpr _Head_base(const _Head& __h)
       : _M_head_impl(__h) { }
 
-      template<typename _UHead, typename = typename
-	       enable_if<!is_convertible<_UHead,
-	                                 __uses_alloc_base>::value>::type>
+      constexpr _Head_base(const _Head_base&) = default;
+      constexpr _Head_base(_Head_base&&) = default;
+
+      template<typename _UHead>
         constexpr _Head_base(_UHead&& __h)
 	: _M_head_impl(std::forward<_UHead>(__h)) { }
 
-      _Head_base(__uses_alloc0)
+      _Head_base(allocator_arg_t, __uses_alloc0)
       : _M_head_impl() { }
 
       template<typename _Alloc>
-	_Head_base(__uses_alloc1<_Alloc> __a)
+	_Head_base(allocator_arg_t, __uses_alloc1<_Alloc> __a)
 	: _M_head_impl(allocator_arg, *__a._M_a) { }
 
       template<typename _Alloc>
-	_Head_base(__uses_alloc2<_Alloc> __a)
+	_Head_base(allocator_arg_t, __uses_alloc2<_Alloc> __a)
 	: _M_head_impl(*__a._M_a) { }
 
       template<typename _UHead>
@@ -258,7 +260,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       template<typename _Alloc>
 	_Tuple_impl(allocator_arg_t __tag, const _Alloc& __a)
 	: _Inherited(__tag, __a),
-          _Base(__use_alloc<_Head>(__a)) { }
+          _Base(__tag, __use_alloc<_Head>(__a)) { }
 
       template<typename _Alloc>
 	_Tuple_impl(allocator_arg_t __tag, const _Alloc& __a,
diff --git a/libstdc++-v3/testsuite/20_util/tuple/61947.cc b/libstdc++-v3/testsuite/20_util/tuple/61947.cc
new file mode 100644
index 0000000..7e77de6
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/tuple/61947.cc
@@ -0,0 +1,29 @@
+// { dg-options "-std=gnu++11" }
+// { dg-do compile }
+
+// Copyright (C) 2014 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+#include <tuple>
+
+struct ConvertibleToAny {
+  template <class T> operator T() const { return T(); }
+};
+
+int main() {
+  std::tuple<ConvertibleToAny&&> t(ConvertibleToAny{});
+}
diff --git a/libstdc++-v3/testsuite/20_util/uses_allocator/cons_neg.cc b/libstdc++-v3/testsuite/20_util/uses_allocator/cons_neg.cc
index cf5d6a57..6396e26 100644
--- a/libstdc++-v3/testsuite/20_util/uses_allocator/cons_neg.cc
+++ b/libstdc++-v3/testsuite/20_util/uses_allocator/cons_neg.cc
@@ -44,4 +44,4 @@ void test01()
 
   tuple<Type> t(allocator_arg, a, 1);
 }
-// { dg-error "no matching function" "" { target *-*-* } 91 }
+// { dg-error "no matching function" "" { target *-*-* } 92 }